1. Field of the Invention
The present invention relates to a three-dimensional measurement apparatus capable of calibrating an apparatus error that occurs in the three-dimensional measurement apparatus for measuring the surface shape of an object, a three-dimensional measurement method, and a storage medium.
2. Description of the Related Art
As an apparatus for measuring the surface shape of an object in a noncontact manner, there is conventionally an apparatus that measures the surface shape based on the principle of the triangulation method using a projection unit and a capture unit. This measurement method will be described. First, the projection unit projects a pattern onto the object. Next, the capture unit captures the object with the projected pattern. The position of the pattern on the capture pixel surface of the capture unit is detected from the captured image data. Then, positions on the pattern on the projection pixel surface of the projection unit and positions on the pattern on the capture pixel surface are made to correspond with each other.
The positional relationship between the projection unit and the capture unit is obtained by calibration. For example, the base line length between the projection unit and the capture unit, the rotation/translation information of the capture unit and the projection unit, apparatus specific parameters of the projection unit and the capture unit, the focal length, the optical axis principal point position, the lens aberration values, and the like (to be generically referred to as calibration values) are obtained in advance.
Finally, the distance from the apparatus to the object is measured from the calibration values and the positional relationship between the pattern on the projection pixel surface and that on the capture pixel surface using the principle of the triangulation method. In the apparatus that measures the surface shape of an object using the projection unit and the capture unit, generally, the shapes and arrangement of the devices in use slightly change over time due to, for example, a thermal expansion/contraction effect associated with temperature changes. For this reason, if the temperature readily changes in the measurement environment or the measurement is performed for a long time, the pattern projection position slightly changes. This leads to an error in the result of the surface shape even when the same object is measured under the same conditions.
To solve this problem, Japanese Patent Laid-Open No. 8-054234 proposes a method of calibrating three parameters, that is, the base line length, the projection angle of a projection unit, and the capture angle of a capture unit by arranging a plurality of targets whose distances from a three-dimensional measurement apparatus are accurately known. Japanese Patent Laid-Open No. 5-248830 proposes a method of performing calibration by splitting a measurement beam projected from a projection unit into a three-dimensional measurement apparatus and obtaining the difference between a beam projection position stored in advance and the projection position of the split beam.
In Japanese Patent Laid-Open No. 8-054234, however, the distance between each target and the apparatus needs to be known accurately, and setup in the actual operation is cumbersome. In addition, since the distance between each target and the apparatus itself may change over time, the reliability of calibration values is low. In Japanese Patent Laid-Open No. 5-248830, a new device is added into the apparatus. This poses problems in downsizing and cost of the apparatus.